EP0304588B1 - Process for the production of heat-insulating full and hollow bricks from fluidized-bed residues - Google Patents

Description

The invention relates to a method for producing heat-insulating solid and perforated bricks of low bulk density from residues of fluidized bed combustion plants which are operated with ballast-containing hard coal, the fluidized bed filter ash being mixed with boiler ash and hydrated lime with the addition of water and then being shaped and pressed into stones, in order then to be hardened .

The possible uses of fluidized bed ash, especially filter ash, are limited and pose considerable problems because these ashes are contaminated due to the specific type of sulfur incorporation and the reaction products of the desulfurization process as well as residual amounts of unused deacidified lime. It has been found that the material undergoes a considerable elongation or volume increase, which is between 14.7 and 17.1% in swelling tests without load. This considerable expansion only occurs after a rest period of more than 2 to 4 hours. Another significant limitation of the usability lies in the fine grain size of the filter ash, because around 70% of this residue has a grain size that is <63 µ.

It has already been proposed to use the fluidized bed filter ash for the production of cement-bound solid or the like. Use stones (U.S. Patent 4,344,796). However, it has been found that the material poses considerable problems for processing with cement in conventional mortar and concrete mixtures, particularly because of the change in setting times, because of the anhydrite content which is activated by the residual lime when water enters. In addition, the material cannot be molded and hardened properly. The stones made from it do not meet the standards.

In production trials using the known lime sand process, problems occurred during molding of the stones due to the specific properties of the material, which are characterized by defects in the pressed blanks and by cracks before the hardening process. The missing parts are primarily due to the fact that the material is not free-flowing due to the fineness of the grain and can therefore not be filled to fill the tool, on the other hand, the fine-grained nature hinders the ventilation of the pressed material.

It was therefore necessary to solve the problems described. The invention is therefore based on the object, when using finest-grain filter ash from fluidized bed combustion plants in the production process of steam-hardened stones, to process the highest possible proportion of fluidized-bed residues and to produce flawless stones in the process.

The object is achieved in that the fluidized bed filter ash <1 mm to prevent the inclusion of compressed air in the subsequent pressing with coarse sand of the bed and kettle ash 1.0 to 5 mm from these fluidized bed plants or similarly dense minerals with the same grain size, with the addition of hydrated lime Inclusion of the active lime content of the ashes brought to a total binder or reactant content of approx. 10% by weight and mixed at a moisture level of 11 to 14%, homogenized and then with ventilation of the mixture to solid and / or perforated bricks or wall blocks compressed and then cured at about 180 ° C for a period of 4 hours, the heating of the pressure vessel over 2 hours and the pressure reduction is also extended to 2 hours.

Surprisingly, it has been found that if such a preparation and treatment method is followed, stones can be produced which have sufficient strength and at the same time advantageous stone densities. Above all, it is possible with this method according to the invention to process considerable amounts of the fluidized-bed residues containing anhydrite and lime, which had previously only had to be disposed of in hazardous waste landfills, the otherwise troublesome lime content (up to 6% by weight) advantageously being used for the process becomes. By adding the larger one Material, ie the coarse sand, prevents the formation of cracks, because compression of the air contained in the mixture is avoided by the changed structure of the mixture granulation. Despite the small amount of additional lime, by setting the moisture to a value between 10 and 15% while reducing the pressing speed, it is possible to produce full, perforated or wall blocks that can be easily removed from the mold and hardened effectively after the compression process . The advantageous end values of strength with significant weight savings (up to 25% by weight based on stones of the same size made from natural sand) have surprisingly proven that fine-grained residue material that tends to swell can be the starting material for improved building materials or building materials with appropriate treatment.

It has been found that optimum process conditions are present if the dry mixture of solid bricks with the desired compressive strength above 12 N / mm² is produced from 60 to 70% by weight of fluidized bed filter ash and 30 to 40% by weight of coarse sand, which is then the 10th % By weight of missing active lime in the form of CaO or Ca (OH) ₂ is added and the moisture content is adjusted to 12.5%. If these process conditions are observed, the solid stone formats 2 DF and 3 DF, form-stable products, in which no hair-like relief cracks occur after compacting. The stone series produced in this way have an average stone bulk density of 1.3 to 1.4 kg / dm³ with an average compressive strength of approx. 12 N / mm².

Due to the gentle pressure build-up of the saturated steam conditions in the autoclave, an optimally hardened production is possible, which fulfills the required building physical conditions perfectly. In addition, the invention provides that the pressure build-up is set between 110 and 150 bar during hardening. The stones thus produced advantageously fulfill the conditions placed on such products.

When producing 2 DF and 3 DF perforated bricks, the pressing process can be carried out at only slightly reduced pressing speeds due to the better ventilation provided by the perforation. Optimal utilization of the machine capacity, which is essentially influenced by the pressing speed, is given when fluidized bed filter ash <1 mm and coarse sand in the form of bed ash from fluidized bed systems or power plant boiler ash in grain size 1 to 5 mm in a ratio of 3: 2 to the dry mix be involved. It has been shown that combinations of power plant ash and bed ash of the fluidized bed are also possible with one another, so that the grain size found from residues of other hard coal combustion plants can be used advantageously with an unbalanced disposal balance. Accordingly, it is provided that the proportion of the coarse sand of the bed and boiler ash is completely or partially replaced by power plant ash with a grain size of 1 to 5 mm.

If the build-up of higher pressing pressures is desired or if a higher density of the stone material is to be achieved, the invention provides for the proportion of coarse sand in the bed and kettle ash to be completely or partially replaced by natural sand 1.0 to 2 mm, in particular for formats up to 3 DF.

If the goal is to achieve a low stone bulk density, the use of natural sand is inappropriate due to the higher bulk density and should be discarded in favor of the use of bed ash from fluidized bed combustion systems or their substitute. For stone formats that correspond to the dimensions 10 or 12 DF or for large-format wall components, it is advisable to use only coarse sand from combustion residues in the for reasons of ventilation but also to save weight Use grain size 1 to 5 mm.

With large-sized stones, the ventilation problem poses special requirements. In addition to the coarsening of the material to be pressed, it has proven to be effective to reduce the pressing speed to such an extent that the air contained in the mixture can escape before the highest stamp pressure is reached. A pressing speed is advantageous, in which the stroke speed is adjusted from 8.5 to up to 15 sec / stroke. Of course, the degree of the pressing speed depends on the size of the stones to be produced. Accordingly, it is provided according to the invention that the pressing speed is increased with increasing coarsening of the aggregate. On the other hand, the pressing speed is naturally lower for large stones or large dimensions than for smaller solid or perforated stones. This gives the skilled person a lesson on how to proceed according to the circumstances in order to obtain optimal products. As already described, the possibility of producing large-format wall blocks by the process according to the invention is also that the fluidized bed filter ash with two parts and the coarse sand with three parts goes into the dry mixture. This achieves a further improvement in the grain structure, as a result of which the pressing speed can be increased to 10 seconds / stroke at the expense of the disposal concern. Overall, requirements of strength class 12 can be set, so that these wall blocks can also be used for high quality requirements.

The invention is characterized in particular by the fact that a method is created with which heat-insulating, steam-hardened shaped bricks can be produced which are lighter in weight than the bricks customary hitherto, that is to say are easier and easier to handle than the same size Stones in a conventional mix. The large formats, ie wall blocks from a stone length of 50 cm with a stone height of 23.8 cm for a 17.5 mm wall, must already be processed with moving aids, generally using a hand crane, because they increase the permissible individual weight of 24 kg by up to 20% exceed. The stones of the same size manufactured according to the method weigh only 21.0 kg and have a stone bulk density of 0.99 or 1.0 kg / dm³.

The following explanation of the single figure, as well as the examples and experiments given for the process according to the invention, serve to clarify the process and the location of the ash and the causes of the active lime constituents of the reaction products in the residues.

In the single figure, the fluidized bed reactor is denoted by (1), to which a waste heat boiler (2) is connected. In the fluidized bed, fuel is introduced from a coal bunker (3), and the necessary additives from a lime bunker (4) via a transport device (5). The air necessary for the operation of the fluidized bed reaches the fluidized bed reactor (1) via the line (6).

The bed ash obtained in the fluidized bed reactor (1) is collected in the ash container (7) and discharged. The exhaust gases, which are around 900 ° C, enter the waste heat boiler (2), in the boiler bottom (8) of which boiler ash is deposited and also discharged. The hot exhaust gases from the waste heat boiler (2) pass through a channel (9) into a bag filter (10) in which the fly ash (11) is separated. The ashes are removed separately and bunkered into two groups in the application shown. The first group comprises the filter ash with a grain size of <1 mm, the second group includes the kettle ash with a grain size of 1.0 to 5 mm and the sieved grain particles of the bed ash <5 mm.

In general, the ashes are processed by the user, which is usually a sand-lime brick plant. There, the ashes are blown into silos and, if necessary, compiled and leveled with boiler ash in the grain size 1.0 to 5 mm or with quartz sand in the grain size 1.0 to 2.0 mm. The individual mixed products reach the mixer (17) from the bunkers (13, 14, 15) (quartz sand, bed ash, filter ash) and from the lime storage bunker (16), where they are mixed evenly and adjusted to a certain humidity. From there it is stored in the reactor (18), where the lime is extinguished. The press moisture in the post-mixer (19) is then corrected and the mixed product is compressed in the press (20), the compression speed being able to be influenced as required by the stroke speed of the ram (21) of the press (20).

The appropriately preformed and de-energized solid bricks, perforated bricks or wall blocks are further treated and hardened in the autoclave (22) and then brought to the storage location from which they can be brought to the respective consumers.

EXAMPLE I

For the production of 2 DF and 3 DF solid bricks, which have a stone height of 10.8 cm, appropriate molding tools were installed in the presses.

The starting mixture had the following recipe: Fluidized bed ash 41.2 kg Quartz sand (1.0 to 2 mm) 15.8 kg Dry surcharge 57.0 kg Lime content taking into account the self-lime of the dry mix 3.99 kg Set humidity 12.5% Pressure build-up 119 to 150 bar Lifting speed 8.5 sec / stroke

The blanks produced could be pressed perfectly and remained dimensionally stable. The stone bulk density was 1.31 kg / dm³, the average compressive strength was 10.98 N / mm².

EXAMPLE II

A mixture of the following components was used to manufacture perforated bricks in the 2 DF format: Fluidized bed ash 120 kg Coarse sand from kettle ash 1, o to 5 mm 45 kg Surcharge amount, dry 165 kg Lime taking into account the self-lime quantity of the mixture 15 kg Set humidity 12.5% Lifting speed 10.5 sec / stroke

EXAMPLE IIa

In order to better utilize the capacity of the press, an attempt was made to increase the lifting speed. It turned out, however, that despite the small press volume, the deformation results were worse. Therefore, the basic mixture was coarsened by adding kettle ash. Three parts of the starting formulation mentioned in Example II were supplemented by a part of boiler ash. The lime content was then increased to a total of 10%, including the self-lime quantity of the fly ash, and the press moisture to 12.5%. set. The pressing takes place at a stroke speed of 8.5 sec / stroke.

In the course of further experiments, it was found that a mixture in which the mixing ratio of the aggregate components of fluidized bed ash to coarse sand is 3: 2 must be used under these pressing conditions, such as were used when using natural sand. Otherwise, the conditions described above can be met. The result of the coarsening of the mix at the press speed increased to 8.5 sec / stroke was quite satisfactory. The stones not only showed perfect shape, they also detached from the molds without any problems and could be easily transported to the stacking belt with the removal devices and further lifted from the stack onto the hardening trolleys.

The fact that this manufacturing result can be achieved with almost normal machine performance can be regarded as a favorable prerequisite for an operational application of the method according to the invention. The building physics mean values of this stone series were with a stone density of 1.1 kg / dm³ and a compressive strength of 8.5 N / mm². The comparison with the compressive strength achieved with solid bricks shows the extraordinarily good result with regard to the ratio of bulk density to resilience.
The favorable results in the production of perforated bricks in the 2 DF format prompted the company to test the manufacture of large-format wall components using the developed process steps.

EXAMPLE III

During the production of the large-format wall blocks in the dimensions 50 x 17.5 x 23.8 cm, the mixture of the Example IIa used with: Fluidized bed ash 120 kg Coarse sand from kettle ash 1, o to 5 mm 80 kg Surcharge amount, dry 200 kg Lime taking into account the amount of self-lime in the mixture 18.2 kg Set humidity 12.5% Lifting speed 10.5 sec / stroke

The height of the format made it necessary to further reduce the already reduced pressing speed from 10.5 to 15 seconds / stroke. The stones pressed at the original speed showed defects in the stone cover, which were blown off by the explosively escaping compressed air. When the press speed was reduced to the 15 sec / stroke already mentioned, the blanks produced were absolutely stable and sharp. They could be handled and transported perfectly by the automatic removal devices and survived the hardening process without defects.

With an external stone volume of 20.825 dm³, the stone bulk density of around 1.0 kg / dm³ was determined. By using the light surcharges described, it was possible to reduce the total weight of the wall component to 21 kg. Despite the low stone bulk density, the compressive strength of the stone was i.M. 12 N / mm² and was therefore in a favorable area of use.

In further experiments with which the reduction in the pressing speed was to be tested, it was found that the pressing frequency can be increased to 10 sec / stroke if the mixture proportions are 40% fluidized bed filter ash and 60% coarse sand in the form of kettle ash with a grain size of 1.0 to 5 mm.

However, it cannot be the aim of the method according to the invention to simplify the production conditions by progressively reducing the filter ash content. Rather, the aim was to make the highest possible proportions of fine-grain grains, at which soil mechanical permeability values k _f measured between 3.5 and 4.2 x 10⁻⁷ m / sec, usable in areas of use in which the lime content including it Reaction products do not interfere with the use, but on the contrary favored by saving lime. In this sense, it is important to note that it was not only possible to incorporate high proportions of the fluidized bed filter ash into the process under the conditions described, but that it was particularly surprising that the widely differing setting times of lime and activated anhydrite by means of hydrothermal hardening to summarize that there is no mutual impairment and subsequent post-reaction (swelling process).

Claims (9)

1. A method of producing heat insulating solid and perforated blocks of low crude density from residues from fluidised bed firing systems which are operated with inerts-containing hard coal, the fluidised bed firing ash being mixed with boiler ash and calcium hydroxide, with the addition of water and then shaped and pressed into blocks to be hardened, characterised in that the fluidised bed filter ash is less than 1 mm granular size to prevent the inclusion of compressed air during subsequent pressing together with coarse sand and the bed and boiler ash of 1 to 5 mm from these fluidised bed installations, or equally dense mineral substances of the same granular range, with the addition of calcium hydroxide to bring the active lime content of the ash to a total proportion of binder or reactive agent of approx. 10% by weight, the moisture content being adjusted to 11 to 14% whereupon the batch is mixed, homogenised and then, with the exclusion of air, compressed to form solid and/or perforated blocks or wall blocks and then hardened at approx. 180°C over a period of 4 hours, the heating up of the pressure vessel extending over 2 hours and the pressure abatement likewise being extended over 2 hours.
2. A method according to Claim 1, characterised in that the dry mixture is made up of 60 to 70% fluidised bed filter ash and 50 to 40% coarse sand, the active lime lacking to produce 10% by weight being added in the form of CaO or Ca(OH)², a moisture content of 12.5% being adjusted.
3. A method according to Claim 1, characterised in that the pressure build-up during hardening is adjusted to between 110 and 150 bars.
4. A method according to Claim 1, characterised in that the proportion of coarse sand in the bed and boiler ash is partially or entirely replaced by power station ash having a granular size of 1 to 5 mm.
5. A method according to Claim 1, characterised in that the proportion of coarse sand in the bed and boiler ash is wholly or partially replaced by natural sand of 1 to 2 mm.
6. A method according to Claim 1, characterised in that the pressing rate is increased with increasing coarseness of the additives.
7. A method according to Claim 4 or Claim 5, characterised in that fluidised bed ash and coarse sand are used in a proportion of 3:2.
8. A method according to Claim 1 to Claim 7, characterised in that the pressing rate is adapted from 8.5 up to 15 secs/stroke.
9. A method according to Claim 8, characterised in that the pressing speed is reduced as the block format increases, preferably to 12 to 15 secs/stroke.

Images